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TOPIC: Re: 3-way open baffle (and subwoofer)

3-way open baffle (and subwoofer) 6 years 8 months ago #7922

  • sladi
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Hi, after adding a potentiometer to the MiniDSP - an option which I had forgotten for some time - I can consider my project somewhat complete. I wanted to build my own amplifier using some Albs MOS-100N modules I got, but for now this is adequate. I got lucky and found some nice used amps, and the speakers were lying around without much use for a long time too.

The constuction is like those bridges, using fairly thin wood "sticks" pulled by steel cables and some aluminium tubes for left to right reinforcement. The base is not very nice, so I didn't make a photo, but it is a wooden box filled with stone, basically. The goal was to lower the center of gravity. So far it hasn't self destructed yet.

amplification
The tweeter and mid sections are powered by a WPA-600PRO with about 80W each. The woofer has a db-Technologies MPA-204 in bridge mode, about 200W into 8 Ohms. The subwoofers for now will operate with an old Technics SA-500, but the bass reflex cabinets will be large and thus needing less than 20 Watts each.

source
The source is a PC, an X-Fi Xtrememusic, which is connected to a couple of 2.2kOhm resistors to get a summed mono signal. Unfortunately since Vista there is no global mono setting in Windows anymore. Luckily I hadn't any 50Hz hum, but the power for the soundcard is polluted by the CPU and graphics card, so I got unacceptable noise. I tried creating a grounded aluminium foil shield for the soundcard, which lowered the noise level a bit. It was still to high when listening at low levels, so I bought an optical isolation amplifier kit from the site "ELV". Now when I put my ear next to the speaker, I can hear a low level of noise from that amplifier, very nice.

why
When I saw the Orion speakers by Sigfried Linkwitz, I wanted to try the concept. After finding the MiniDSP however I was confident I could do it.

why2
I don't have a lot of room and I don't like being confined to a Stereo triangle either. So I built one big speaker instead of multiple smaller ones. The increased cone area certainly is nice. Before I had a 5.1 setup and I haven't missed it in the confinements of a smallish flat. Certainly the stereo effect is not the end all be all, and your brain imagines surprisng levels of directionality when watchin some movie from a single speaker.


slightly technical
The whole setup is meant to give about 105dB/1m with a little bit of headroom to xmax of the drivers, although the amplifiers may be too weak to max the drivers out completely. I looked for nicely behaved drivers for the intended passbands because I do not have a measurement setup. All is setup by ear, theory and simulation programs like BASTA.


I tried to maintain dipole behaviour for each driver, and targeting lower SPL it was easier than for the Orion:

The tweeter is a 2" Monacor SPX-20M with a relatively large coil diameter of 25mm. Its cone finish actually matches the midrange nicely. It is crossed at 1900Hz 4th order LR.

The midrange is a Seas MCA12RC H1304. It's got a nice back ventilated construction, but being only in a baffle, the coil is a bit exposed. Its highpass is at 500Hz.

The woofer is a 12" Beyma 12 LX60, which I also luckily got second hand. Currently it is highpassed at 50Hz but when my subwoofers are complete, it will be crossed at 90-100Hz 24dB LR.

The subwoofers should be two 12" Beyma BR70 in 140 litres bass enclosures tuned at about 25Hz. The Beyma was my first buy as the woofer for the 3-way, but luckily I got a much nicer one, so I bought another one to get two identical subs. I calculated about 6-10dB headroome relative to the main speaker, and I wonder how the result in my room will be.


MiniDSP 2x4 with 3-way plugin
I am using the biquad filters to recreate Linkwitz's filter chain, so the midrange gets the highpass filters of the sub and woofer too, to avoid phase erros. For the tweeter it is just enough, since two 24dB filters from bass and mid take up four filters already. In order to "save" one filter, I apply the first highpass for the sub in the general PEQ filter section instead of the crossover section. This way it automatically gets applied to all channels (I hope :) ).

The speaker sounds nice, the best I ever had certainly - and the most expensive setup too of course. The dynamics are great and the drivers seem to be a nice match for each other. None is getting bad at higher volumes before the others. I hope the subwoofer will be that nice too.
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Re: 3-way open baffle (and subwoofer) 6 years 8 months ago #7924

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Can't edit, but I wanted to add that the woofer position on top results in all drivers operating in 4pi space. Also the drivers are mounted staggered so their acoustic centres roughly match.
Last Edit: 6 years 8 months ago by sladi.
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Re: 3-way open baffle (and subwoofer) 6 years 7 months ago #8013

  • devteam
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Great Stuff Lom! Quite a unique setup with the drivers hanging this way! Were you inspired by a specific setup/simulation?

Cool stuff to see creative ideas and glad to see that you're happy with your finished install!

Have fun
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MiniDSP, building a DIY DSP community one board at a time.
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Re: 3-way open baffle (and subwoofer) 6 years 7 months ago #8116

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Thanks, yes I was inspired by the Orion loudspeakers by Siegfried Linkwitz. I wondered if I could do a similar setup using less expensive drivers and by lowering the SPL capability to be more flat friendly (about 6dB less). So far it seems to work, it was interesting to see if all this theory would work out, it is my first DIY speaker, obciously made a lot easier using the Minidsp.

Now I finally finished one 70 litre bassreflex subwoofer using a Beyma BR70 (I have two of those and enough room :) ), and I am alternating between having a crossover to the main speaker at 190Hz or at 90-100Hz. I will have to see how the subwoofer sounds compared to the 12LX60 higher up. The power requirement would go down - and I can place the sub right behind the main speaker too. :)
Last Edit: 6 years 7 months ago by sladi.
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Re: 3-way open baffle (and subwoofer) 6 years 7 months ago #8142

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A nicer way to build it would habve been using bamboo, I guess. I hope I will have time to do that some time. :)
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